Trifluoroketones are used as precursors for synthesis of tryptophan hydroxylase (TPH)-inhibiting compounds, such as those described in U.S. Pat. No. 9,199,994 (De Lombaert et al.), issued Dec. 1, 2015. These TPH-inhibiting compounds are useful in the treatment of diseases or disorders associated with peripheral serotonin including, for example, gastrointestinal, cardiovascular, pulmonary, inflammatory, metabolic, and low bone mass diseases, as well as serotonin syndrome, and cancer.